Gas turbine engines may be subject to reduced performance at some point in their service lives. There may be many causes for this reduced performance, including engine component wear, accessory faults, or internal instrumentation errors. When gas turbine engines are used in aircraft, any occurrence of reduced performance must be promptly diagnosed and corrected, before the aircraft can be returned to service. However, the engine performance instrumentation provided on the aircraft, while adequate for flight management proposes, is generally incapable of providing sufficient information to diagnose some types of performance problems. One problem is that the aircraft instrumentation does not measure all the types of data needed to pinpoint the source of the problem; another problem may be that the aircraft instrumentation is itself in error. This lack of sufficient reliable data to pinpoint the problem often results in guessing at the needed corrective action, and may involve expensive removal of modules or the entire engine, to determine the problem. Incorrect guesses at corrective action can lead to added expenses in the process of eventually finding and correcting the problem.
Various systems or devices have been proposed in the prior art to improve on this situation. Such prior art systems often involve data recorder or computer packages to work with various sensors for attachment to the aircraft engine, with connections and transducers to monitor engine parameters such as speed, torque, turbine temperature, as well as fuel, oil and electrical parameters. Some also measure pressure and temperature at the compressor intake and discharge so that compressor efficiency can be calculated. Such systems usually accomplish this by measuring static pressure and temperature through any available port at the compressor discharge. However, this is insufficient information to calculate mass air flow since one also needs to know the station total pressure and the cross-sectional flow area to some accuracy. It will therefore be appreciated that, such prior art systems do not provide direct measurement of gas path data, but only provide an indirect indication thereof by tracking the other parameters over time, from which one may be able to infer insufficient mass flow.
Of course it is known in the field of gas turbine design and development to provide instrumentation to measure mass airflow, as well as many other parameters, as an aid in the development testing of new engines. This type of testing often involves elaborate and expensive testing facilities and specially instrumented prototypes which are very useful in the engine development environment, but which are impractical in the field.